Recently, the functional properties of oligosaccharides have been revealed and practically used respectively in various use of foods, pharmaceuticals, etc. Among these oligosaccharides, non-reducing oligosaccharides having a β-fructofuranosidic linkage have, as a characteristic property, a preferable feature relatively close to sugar (or sucrose) in term of sweetness or the like; and they are used in the following as main ingredients that exert various functions: For example, lactosucrose, where galactose is bound to the glucose residue of sucrose via the β-1,4 linkage, which has substantially-hard digestibility, bifid-bacterium-growth-promoting property, substantially-free cariogenicity, and moisture-retaining ability; glycosylsucrose, where glucose or maltooligosaccharide is bound to the glucose residue of sucrose, which has crystallization-preventing action on sugar, moisture-retaining ability, and substantially-free cariogenicity; and fructooligosaccharide, where fructose or fructooligosaccharide is bound to the fructose residue of sucrose via the β-1,2 linkage, which is easily assimilated by bifid bacteria and capable of improving intestinal flora have been used in food products, cosmetics, and pharmaceuticals for the purpose of, for example, improving physical properties, improving taste, inhibiting cariogenicity, improving bacterial flora, and controlling immunity.
As disclosed in, for example, Japanese Patent Kokai No. 224,665/97, lactosucrose is prepared by allowing a β-fructofuranosidase derived from a microorganism to act on a solution containing sucrose and lactose through saccharide-transferring reaction catalyzed by the β-fructofuranosidase. As disclosed in, for example, Japanese Patent Kokoku No. 17,660/78, glycosylsucrose is prepared by allowing a cyclomaltodextrin glucanotransferase derived from a microorganism to act on a solution containing sucrose and partial starch hydrolyzate. As disclosed in, for example, Japanese Patent Kokai No. 201,980/83, fructooligosaccharide is prepared by allowing a β-fructofuranosidase derived from a microorganism to act on sucrose.
As disclosed in the above Japanese Patent Kokai No. 224,665/97, Japanese Patent Kokoku No. 017,660/78, and Japanese Patent Kokai No. 201,980/83, a non-reducing oligosaccharide having a β-fructofuranosidic linkage is prepared by allowing a saccharide-transferring enzyme to act on an oligosaccharide containing sucrose through a saccharide-transferring reaction from an oligosaccharide to another oligosaccharide. In practicing the reaction, the objective non-reducing oligosaccharide, which consists of a tri-saccharide or higher having a β-fructofuranosidic linkage, is formed along with, for example, one or more reducing saccharides selected from glucose, fructose, galactose, maltose, lactose, and maltotriose, which are inevitably formed as by-products.
The objective non-reducing oligosaccharide has been commercialized in the market as a syrupy sweetener product after the non-reducing oligosaccharide coexisted with the above by-products is subjected to purification steps such as decoloration with an activated charcoal and desalting with ion-exchange resins in H- and OH-form. Such a syrupy sweetener, which contains a reducing saccharide together with a non-reducing oligosaccharide having a β-fructofuranosidic linkage, has been revealed to have a defect of being easily colored through deterioration and browning during storage at ambient temperature. To avoid such a defect as much as possible, a cold storage is needed, however, such a cooling increases both the viscosity of the syrupy sweetener and the transportation/storage cost as the drawbacks.
As a method for stably keeping lactosucrose in a lactosucrose-containing-composition for inhibiting abdominal abnormality, for example, Japanese Patent Kokai No. 265,390/98 proposes to adjust the pH to a level of 6.6 to 7.5 by using an organic acid or the like, or a salt thereof as a pH buffer. The method keeps lactosucrose stably, however, it easily causes coloration and loses the product value of a syrupy sweetener containing a reducing saccharide together with a non-reducing oligosaccharide having a β-fructofuranosidic linkage when applied thereunto. Further, it was also revealed that the preferable sweetness inherent to the syrupy sweetener is deteriorated to lose its product value as a sweetener by the unsatisfactory taste such as salty and astringent taste inherent to the organic acid or the like and the salt thereof used as a pH buffer.